Animal waste poses a significant problem in the poultry, swine and cattle industries. Animal waste from animal raising or processing operations is responsible for a significant amount of underground water contamination and methods are continually being developed for handling animal wastes. One known method is the bioconversion of animal waste into useful products.
Methods for the anaerobic digestion or treatment of sludge, animal waste, synthesis gas or cellulose-containing waste are disclosed in U.S. Pat. No. 5,906,931 to Nilsson et al., No. 5,863,434 to Masse et al., No. 5,821,111 to Grady et al. No. 5,746,919 to Dague et al., No. 5,709,796 to Fuqua et al., No. 5,626,755 to Keyser et al., No. 5,567,325 to Townsley et al., No. 5,525,229 to Shih, No. 5,464,766 to Bruno, No. 5,143,835 to Nakatsugawa et al., No. 4,735,724 to Chynoweth, No. 4,676,906 to Crawford et al., No. 4,529,513 to McLennan, No. 4,503,154 to Paton, No. 4,372,856 to Morrison, No. 4,157,958 to Chow, and No. 4,067,801 to Ishida et al. These patents disclose different processes and equipment for the bioconversion, either by microbial digestion or enzymatic conversion, of those materials into methane and other useful materials.
The equipment used for the anaerobic digestion or fermentation of waste into fuel, such as methane, varies greatly and is generally tailored to specific applications. Equipment that is suitable for a first type of feedstock generally has to be modified before it can be used for a second different type of feedstock.
Chemical and biochemical reactions that create a gas are generally conducted at low to subatmospheric pressures due to the tendency of the product gas to function as feedback inhibitor that inhibits further formation of the gas. The art recognizes that variations in the pressure of an anaerobic digester can be used to effect different biochemical and productivity results. U.S. Pat. No. 4,409,102 to Tanner discloses an anaerobic digestion conducted at subatmospheric pressures which unexpectedly effects an increase in methane gas production. U.S. Pat. No. 3,994,780 to Klass et al. discloses the high pressure rupture of cells in an anaerobic digester to render cellular components available to other intact cells in the digester. U.S. Pat. No. 3,981,800 to Ort discloses a process for preparing high quality methane (about 98% wt.) with an anaerobic digester operated at 1-5 atm. above atmospheric pressure provided that the sludge is degassed by a recirculator and passed between two digesters to remove carbon dioxide in the sludge which is then fed back into the digester. U.S. Pat. No. 4,100,023 to McDonald discloses that the internal pressure of the anaerobic digester should be kept at about 1 to 3 inches of water column to ensure proper performance. U.S. Pat. No. 4,568,457 to Sullivan discloses a two-stage anaerobic digester system having an acid forming stage and a methane gas forming stage, wherein the pressure of the gas in the headspace of the two stages can be slightly above atmospheric pressure.
Methanogenic microbes that create methane from carbon and hydrogen containing feedstocks, such as cellulose, animal waste, food processing waste, and sludge, are well known. These microbes have been used in the waste processing industry and are available in their native forms from natural sources or in genetically altered or manipulated forms, which can produce greater amounts of useful materials per unit weight of waste than can unaltered methanogenic bacteria.
To date, no equipment containing the required components as described herein has been disclosed. Further, the improved equipment design and layout of the present invention provides a higher yield of methane and other useful materials than other comparable equipment. Still further, the improved process and equipment of the invention can be used in the poultry, swine, dairy or cattle industries to convert cellulose-containing animal waste into methane which is used to operate farm or ranch equipment thereby reducing operating costs and the volume of waste produced.